HEAT TRANSFER AND FOULING BEHAVIOUR OF SIEMENS PWR STEAM GENERATORS - LONG TERM OPERATING EXPERIENCE

摘要

The evolution of heat transfer performance of the steam generators is regularly monitored on the basis of plant data recordings in many Siemens pressurized water reactors. For the oldest steam generators operating experience covers more than 27 years. Heat transfer performance is quantified in terms of the fouling factor. It is correlated with the amount of iron ingress into the steam generator stemming from the feedwater/steam cycle Since all plants which have started under phosphate treatment have converted their feedwater chemistry to H-AVT treatment (all volatile treatment with hydrazine dosing to assure high pH-values) iron transport in these plants has drastically reduced and consequently fouling increase has almost stopped. In plants which operate under H-AVT from the beginning, no significant fouling factor increase has been observed after up to 15 years of operation. Hence, H-AVT is the preferred feedwater chemistry regime - not only from corrosion prevention point of view but also from heat transfer performance point of view. Thermal effects of chemical cleaning as well as the fouling behaviour specific to economizer type steam generators are also addressed in the paper.